1. Field of the Invention
The present invention relates to a high-frequency transmission line and a dielectric resonator suitable particularly for use in a microwave or millimeter-wave band.
2. Description of the Related Art
Microstrip lines are widely used as transmission lines in high-frequency circuits because of its advantages that they can be easily produced into a small-sized form and/or into a thin form.
As shown in FIG. 33, the basic structure of a microstrip line consists of a ground electrode 2 formed on one surface of a dielectric plate 1 and a microstrip line electrode 3 formed on the other surface. In the microstrip line having such a structure shown in FIG. 33, a current is concentrated on edges of the electrode 3 because of the so-called edge effect. This gives rise to a great increase in the conductor loss at the edges. The great majority of the conductor loss occurs in an edge portion within the range of a few microns of the microstrip line. This means that the loss and the maximum allowable power of the transmission line are dominated by the edge effect.
In view of the above, Japanese Unexamined Patent Publication No. 8-321706 discloses a high-frequency transmission line in which the concentration of a current at edges of an electrode is eased. In this high-frequency transmission line, line-shaped conductors with a fixed width are formed so that they are spaced a fixed distance apart from each other and so that they extend in a direction parallel to a signal propagation direction.
Although the transmission line structure including line-shaped conductors having a fixed width and equally spaced from each other is effective to ease the current concentration at edges, the central portion of the transmission line is also made up of line-shaped conductors and thus an increase in the conductor loss occurs due to the reduction in the effective cross-sectional area of the conductor in the central portion of the transmission line.
The above problem occurs not only in microstrip lines or transmission lines, but also in dielectric resonators consisting of an electrode formed on a dielectric.
In view of the above, the object of the present invention is to provide a high-frequency transmission line and a dielectric resonator formed into a small-sized shape and having an effectively reduced loss.